* tests/actions.at: Test that stack overflow invokes destructors.

* tests/actions.at: Test that stack overflow invokes destructors.
From Marcus Holland-Moritz.
* data/yacc.c (yyerrlab): Move the code that destroys the stack
from here....
(yyreturn): to here.  That way, destructors are called properly
even if the stack overflows, or the user calls YYACCEPT or
YYABORT.  Stack-overflow problem reported by Marcus Holland-Moritz.
(yyoverflowlab): Destroy the lookahead.